The permeablity of electrotonic junctions between embryonic cells will be characterized in terms of molecular size and charge. Long pore effects will be looked for. Changes in selectivity as a result of pH or salicylate will be studied. Area of gap junctions and coupling resistance of individual cell pairs will be determined to allow calculation of single channel values. Changes in junctional resistance will be studied to determine if opening and closing of single channels can be detected. Particle arrays at gap junctions will be studied by freeze fracture during formation and after uncoupling. Fixed and unfixed but cryoprotected cells will be compared. Effects of divalent ions on junctional resistance will be evaluated. Inhibitors of cell movement, e.g. cytochalasin B, will be applied to examine the role of movement in junction formation. Capability of embryonic and adult cells from the same species to form junctions will be evaluated. The goal is to characterize the channels connecting the cell cytoplasms and to analyze the mechanisms involved in their formation and disruption. The experimental systems to be employed are uniquely accessible to the proposed studies. Insight should be provided into the role of these junctions in development and also into their functioning in the adult tissues in which they are so prevalent.